The exteriors of many residential and commercial buildings have long been protected by "finishing" or "sheathing" materials including wood, metal, and polymer resins. Metal sheathing such as aluminum siding was once very popular since it was more insect-and weather-resistant than wood siding and could be anodized, painted, or laminated to provide a plurality of colors and styles. Metal sheathing also proved to be long lasting and energy efficient. However, because it could not be easily sawed, clipped, or drilled with hand tools, it was relatively labor intensive to install. Additionally, metal sheathing materials had to be extremely thin to be cost efficient, and, because of their inherent lack of resiliency, were susceptible to irreversible dents, creases and other damage from minor impact, bending and other loads.
In more recent times, "vinyl siding" (which is typically a resinous composition containing polyvinyl chloride) has provided a less expensive and more impact-resistant material for exterior siding panels. This material can also be provided in a wide variety of colors and patterns, but is more flexible and forgiving and thus does not permanently deform under minor loads. Plastics like polyvinyl chloride are also easy to machine and can be worked with almost any hand tool at the construction site.
It has been found, however, that conventional vinyl siding has not always been satisfactory as an exterior sheathing material for irregular exterior wall surfaces. Due to poor pre-existing construction, material inconsistency, or foundation settling, exterior walls in both new and old constructions are not always flat. Since vinyl siding, as opposed to metal siding, is very flexible, it readily conforms to the irregularities of the wall surface and may produce a crooked, bowed, or otherwise aesthetically unpleasant finish upon installation.
In order to compensate for this deficiency, installers frequently must resort to using wooden shims which must be separately nailed to the support surface before the vinyl siding is installed. Attempts have also been made to loosely nail the siding to the support surface so that the siding "floats" over the uneven portions of the exterior wall. In order to float the siding over the irregularities, but still provide a relatively straight and orderly appearance, the panel must be fairly rigid so as to span high and low points along the wall. Unfortunately, polyvinyl chloride, even in its most rigid state, only has a flexural modulus of about 0.5.times.10.sup.6 psi, and a tensile strength of about one-seventh of that of wrought aluminum.
Synthetic lumber (e.g., polymer-fiber composite lumber) has been used as a substitute for wood in areas where wood deteriorates quickly due to environmental conditions. Although in the past its commercialization was limited by costs, modern recycling techniques and low cost extrusion manufacturing capability have permitted greater penetration by polymer fiber composite materials into the commercial and residential markets. One such product manufactured under the trademark TREX, by Trex Company, LLC, Winchester, VA, consists of a polyethylene and wood fiber blend which is extruded into board dimensions for decking applications. These synthetic wood products are weather resistant and relatively maintenance free. Once installed, they resist splintering and warping normally associated with wood boards. They are also characterized by "color weatherability"; for example, the TREX.RTM. product initially is a light coffee brown color and converts to a weathered gray appearance when exposed to rain water and sunlight.
Polyethylene and wood composite boards do not require painting, and never include knots. Knots often result in damage to the surface of ordinary wood lumber and, usually, more difficult hammering or screwing of fasteners. These composite materials also do not shed sap, and have a smooth surface texture that is comfortable for even barefoot walking. Polyethylene and wood composite boards in 5/4 inch thicknesses such as the "TREX.RTM." board have sufficient rigidity to be used as decking planks. However, they are not suitable for siding or finishing panels because of their bulk and weight and considerable aesthetic dissimilarity to conventional siding panels.
In addition to polyethylene, other plastics have been suggested for use in the manufacture of synthetic wood products. Polyvinyl chloride thermoplastics have been used in combination with wood fibers to make extruded structural members. For instance, U.S. Pat. No. 5,486,553 assigned to Andersen Corporation of Bayport, Minn., discloses such components as substitutes for structural wooden members.
Rigid objects composed of foamed thermoplastic materials are also known. For example, U.S. Pat. Nos. 5,278,198, 5,324,461 and 5,391,585 disclose coextruded articles including a base layer of foamed polyvinyl chloride having at least one non-foamed, thermoplastic (preferably polyvinyl chloride) skin layer adhered thereto. The presence of foam during manufacture of the base layer results in a plurality of open cellular spaces being created in the base layer upon curing. Such voids or spaces reduce the density and weight of the foamed layer. Typically, however, foamed articles are not especially impact resistant. The non-foamed layer(s) provide the protection necessary to render the foamed polyvinyl chloride into viable rigid objects such as pipes and sheets.
Accordingly, a desire exists for a plastic siding panel that is aesthetically pleasing, rugged, resistant to bending or conforming to irregularities in exterior wall surfaces, low in cost, lightweight, and that can be painted or stained as well as worked with ordinary hand tools at the construction site.